Silicon is the basic material for the microelectronics industry. The predicted limits for electrical interconnects in electronic circuits favor the development of alternative solutions such as optical interconnects to transfer information. The silicon-based components are an alternative to realise these interconnections, providing that high speed and high efficiency integrated optoelectronic devices can be realized. In this work, we have fabricated two-dimensional photonic crystal (PC) microcavities on silicon-on-insulator (SOI). The samples contain self-assembled Ge/Si islands deposited in the upper silicon layer by chemical vapor deposition. The silicon layer thickness measures 0.3 mm. The photonic crystals consist of triangular lattices of air holes etched in the upper silicon layer of the SOI substrate. The period lattice measures 0.5 μm and the drilled holes had diameters between 0.3 and 0.45 μm. These structures exhibit a forbidden band around 1.3 - 1.5 μm in TE polarisation. Different photonic crystal hexagonal microcavities were processed and the optical properties are probed at room temperature with the Ge/Si island photoluminescence. Quality factors larger than 200 are measured for hexagonal microcavities. On the one hand, the presence of the PC improves the vertical extraction of light, and on the other hand, we show that a significant enhancement of the Ge/Si island photoluminescence (x 100) can be achieved in the 1.3 - 1.55 μm spectral region using the microcavities. These attractive results should allow to realise efficient light emitting-diodes in the near infrared.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.